This invention relates to new mixtures of polyisocyanates containing basic (tertiary) and/or quaternary nitrogen and having an average NCO functionality of 2.3 to 4.3, to a process for the production of these mixtures and to their use as a starting material in the production of polyurethane plastics or as a crosslinking agent for water-containing polymeric binders.
The significance of water-containing binders for coatings of all kinds is growing steadily on account of stricter emission guidelines and ecological arguments.
Although there are already a number of water-containing binders with a high quality standard, optimal properties can often only be obtained by chemical post-crosslinking during or after film formation.
Aromatic hydrophilically modified polyisocyanates of the type described, for example, in DE-OS 2,359,613 and in EP-A-61,628 are unsuitable for use in water-containing binder systems on account of their high reactivity with water and the resulting emission of carbon dioxide. They are used mainly in the production of foams and in the adhesives field. Isocyanate-functional crosslinking agents for water-based coating systems can only be produced from the less reactive (cyclo)aliphatic polyisocyanates.
EP-A-206,059 describes hydrophilically modified aliphatic polyisocyanates as an additive for water-based adhesives. The emulsifiability of these polyisocyanates is achieved by the incorporation of polyether chains comprising ethylene oxide units. However, polyisocyanates hydrophilicized in this way are only suitable to a limited extent for certain applications on account of the permanent hydrophilic character of the films due to their relatively high polyether content.
The problem addressed by the present invention was to provide new polyisocyanates containing tertiary nitrogen with an (average) NCO functionality of 2.3 to 4.3 which, despite the presence of tertiary nitrogen and isocyanate groups in the same molecule, would be stable in storage, could be dissolved or dispersed in water without difficulty, optionally after at least partial alkylation or protonation, and would be suitable as starting components in the production of polyurethane plastics and, above all, as crosslinking agents for water-containing binders or binder components.
This problem has been solved by the provision of the polyisocyanate mixtures, the process for their production as described hereinafter.